Method for expanding spacings in light-emitting element array and light-emitting element array unit

ABSTRACT

A method for expanding spacings in a light-emitting element array includes the following steps of: providing a light-emitting element array unit including a stretchable supporting film, and a plurality of light-emitting elements disposed on the stretchable supporting film and arranged into a two-dimensional array; stretching the stretchable supporting film along a first direction and a second direction. The first direction and the second direction respectively correspond to a row direction and a column direction of the two-dimensional array.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Patent Application No.103136145, filed on Oct. 20, 2014.

FIELD

The disclosure relates to a method for expanding spacings in alight-emitting element array and a light-emitting element array unit,more particularly to a method for expanding spacings in a light-emittingelement array using a stretchable supporting film, and a light-emittingelement array unit used in the method thereof.

BACKGROUND

The transfer of light-emitting elements, such as LEDs, from an epitaxialsubstrate onto a package substrate, requires high alignment accuracy.Often, the spacing between light-emitting elements on the epitaxialsubstrate does not match the spacing between predetermined positions ofthe package substrate on which light-emitting elements are to bemounted. A conventional approach to this problem has been toindividually transfer each of the light-emitting elements onto thepackage substrate such that adjustments in spacing on the packagesubstrate are possible. However, such conventional method is meticulous,time consuming, and requires relatively high accuracy in aligning thelight-emitting elements onto the package substrate. Moreover,advancements in technology have contributed to a general reduction inthe size of light-emitting elements (such as micro LEDs), demanding aneven higher level of accuracy, and raising the standards in the transferand alignment of light-emitting elements onto package substrates.

SUMMARY

Therefore, an object of the disclosure is to provide a method that canalleviate at least one of the aforesaid drawbacks of the prior art.

According to one aspect of the present disclosure, a method forexpanding spacings in a light-emitting element array includes thefollowing steps of:

providing a light-emitting element array unit including a stretchablesupporting film, and a plurality of light-emitting elements disposed onthe stretchable supporting film and arranged into a two-dimensionalarray; and

stretching the stretchable supporting film along a first direction and asecond direction which respectively correspond to a row direction and acolumn direction of the two-dimensional array.

According to another aspect of the present disclosure, a light-emittingelement array unit used in the method thereof is provided. Thelight-emitting array unit may include a stretchable supporting film, anda plurality of light-emitting elements disposed on the stretchablesupporting film and arranged into a two-dimensional array. Thestretchable supporting film is formed with a plurality of through holesin position corresponding to the light-emitting elements.

In light of the foregoing, by stretching the stretchable supporting filmalong the first direction and/or the second direction ensures uniformspacing of the light-emitting element array along the correspondingdirection(s). Relatively high alignment accuracy can be achievedaccording to the present disclosure while transferring thelight-emitting element array to a package substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiments with reference tothe accompanying drawings, of which:

FIG. 1 is a schematic view showing a light-emitting element array unitused in the exemplary embodiment of a method for expanding spacings in alight-emitting element array according to the present disclosure;

FIG. 2 is a schematic sectional diagram illustrating consecutive stepsof the exemplary embodiment; and

FIG. 3 is a schematic top view showing a variation of the light-emittingelement array unit.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, the exemplary embodiment of a method forexpanding spacings in a light-emitting element array is shown to includeSteps (a) to (c) as follows.

Step (a): providing a light-emitting element array unit 2, whichincludes a stretchable supporting film 21, and a plurality oflight-emitting elements 22 that are disposed on the stretchablesupporting film 21 and that are arranged into a two-dimensional array.

The stretchable supporting film 21 can be made of a flexible polymericmaterial and exhibits adhesive property so as to allow thelight-emitting elements 22 to be adhered thereon. In certainembodiments, the stretchable supporting film may be a blue tape whichallows the light-emitting elements 22 to be easily removed therefrom, alight release tape which has reduced adhesion strength after beingirradiated with light having a predetermined wavelength such as UVlight, or a thermal release tape which has reduced adhesion strengthafter being heated to a predetermined temperature. In this embodiment,the stretchable supporting film 21 is preferably a blue tape to save thetime and cost of the process.

Each of the light-emitting elements 22 has semiconductor layers and isoperable to emit light within a predetermined wavelength range (i.e., toemit green, blue or red light). The dimensions of the light-emittingelements 22, such as height or width, may be identical or different. Itshould be noted that the light-emitting elements 22 may have a widthranging from 1 μm to 100 μm. In certain embodiments, the light-emittingelements 22 may have dimensions ranging from 3 μm to 30 μm, and adistance between two adjacent light-emitting elements 22 may range from2 μm to 25 μm.

In this embodiment, each of the light-emitting elements 22 is configuredinto a geometric shape, such as a quadrilateral shape shown in FIG. 1.As shown in FIG. 1, the light-emitting elements 22 in each row of thetwo-dimensional array are arranged along a row direction, and thelight-emitting elements 22 in each column of the two-dimensional arrayare arranged along a column direction. Adjacent two of thelight-emitting elements 22 in each row of the two-dimensional array arespaced apart from each other by a first spacing (S1), and adjacent twoof the light-emitting elements 22 in each column of the two-dimensionalarray are spaced apart from each other by a second spacing (S2). Itshould be noted that the first and second spacings (S1), (S2) may beidentical or different. In this embodiment, the first and secondspacings (S1), (S2) are identical.

Step (b): stretching the stretchable supporting film 21 along a firstdirection (X) and a second direction (Y) so as to expand the first andsecond spacings (S1), (S2).

Step (b) can be conducted by a stretching apparatus, such as a filmexpander, to stretch the stretchable supporting film 21 along either oneor both of the first direction (X) and the second direction (Y) by apredetermined tensile stress, so as to expand the first spacing (S1)and/or second spacing (S2) to a predetermined value, which maycorrespond to a predetermined spacing suitable for a package substrate.In this preferred embodiment, the first direction (X) and the seconddirection (Y) respectively correspond to the row direction and thecolumn direction of the two-dimensional array of light-emitting elements22. In other words, the stretchable supporting film 21 is stretchedalong either one or both of the row direction and the column directionof the two-dimensional array of the light-emitting elements 22. Itshould be noted that, in this embodiment, Step (b) may be conducted byhaving one side of the stretchable supporting film 21 secured andstretching the stretchable supporting film 21 from the other sidethereof. In other embodiments, Step (b) may be conducted by stretchingthe stretchable supporting film 21 simultaneously from two oppositesides thereof.

In this embodiment, Step (b) is conducted by first stretching thestretchable supporting film 21 along the first direction (X) by a firsttensile stress (P1) so as to expand the first spacing (S1) to anexpanded first spacing (S1′), followed by stretching the stretchablesupporting film 21 along the second direction (Y) by a second tensilestress (P2) to expand the second distance (S2) to an expanded secondspacing (S2′), which may be identical to or different from the expandedfirst spacing (S1′). It should be noted that in certain embodiments,Step (b) may be conducted by first stretching the stretchable supportingfilm 21 along the second direction (Y) and then stretching the samealong the first direction (X). In certain embodiments, Step (b) may beconducted by stretching the stretchable supporting film 21simultaneously along the first and second directions (X), (Y) of the twodimensional array of the light-emitting elements 22.

When the first and second spacings (S1), (S2) are expanded to be theexpanded first and second spacing (S1′), (S2′) by stretching (FIG. 2only shows the stretching of the stretchable supporting film 21 alongthe first direction (X), so that the expanded second spacing (S2′) isnot shown), a step (c) is further provided in this embodiment.

Step (c): attaching a surface of each of the light-emitting elements 22,which are away from the stretchable supporting film 21, onto a packagesubstrate 3, followed by removing the stretchable supporting film 21therefrom.

In this embodiment, the package substrate 3 has a plurality ofconnecting pads 31 that correspond in position to the light-emittingelements 22 on the stretchable supporting film 21 after Step (b). Inother words, the connecting pads 31 are arranged in a manner similar tothat of the light-emitting elements 21 and have spacings respectivelycorresponding to the expanded first and second spacings (S1′), (S2′) ofthe light-emitting elements 22. The package substrate 3 may be, but isnot limited to, a printed circuit board, a TFT substrate, a CMOSsubstrate, a substrate having transistors or integrated circuitsincorporated therein, a substrate having metal redistribution lines orthe like. Each of the connecting pads 31 may be configured as asingle-layered or multi-layered structure and is made of electricallyconductive materials, such as metal materials, non-metal conductivematerials (e.g., conductive polymers, graphite, graphenes and blackphosphorus), or combinations thereof. In certain embodiments, theconnecting pads 31 are made of an alloy material having a eutectic pointlower than 300° C., so that attachment of the light-emitting elements 22onto the connecting pads 31 may be conducted by heating the connectingpads 31 to a temperature above the eutectic point, followed by coolingso as to fixedly attach the light-emitting elements 22 onto theconnecting pads 31 of the package substrate 3.

It should be noted that, in certain embodiments where the stretchablesupporting film 21 is a light release tape (such as UV tape), theremoval of the stretchable supporting film 21 in Step (c) may beconducted by irradiating the stretchable supporting film 21 with a lighthaving a predetermined wavelength (e.g., UV light), so as to reduceadhesion strength between the stretchable supporting film 21 and thelight-emitting elements 22. In addition, in certain embodiments wherethe stretchable supporting film 21 is a thermal release tape, theremoval of the stretchable supporting film 21 from the light-emittingelements 22 in Step (c) may be conducted by heating the stretchablesupporting film 21 so as to reduce adhesion strength between thestretchable supporting film 21 and the light-emitting elements 22. Incertain embodiments where the stretchable supporting film 21 is a bluetape, the removal of the stretchable supporting film 21 in Step (c) maybe conducted by directly peeling off the stretchable supporting film 21from the light-emitting elements 22.

By disposing the light-emitting elements 22 on the stretchablesupporting film 21 and by stretching the same, the first and secondspacings (S1), (S2) among the light-emitting elements 22 in thetwo-dimensional array can be accurately expanded. In addition, thestretching of the stretchable supporting film 21 along the firstdirection (X) and/or the second direction (Y) further ensures uniformspacings of the light-emitting elements 22 along the correspondingdirection(s). As such, relatively high alignment accuracy can beachieved according to the present disclosure while transferring thelight-emitting elements 22, especially when transferring thelight-emitting elements 22 having small dimensions onto the packagesubstrate 3.

FIG. 3 shows a variation of the light-emitting element array unit 2. Inthe variation of the light-emitting element array unit 2, thestretchable supporting film 21 is formed with a plurality of throughholes 23, each corresponding in position to the light-emitting elements22. As shown in FIG. 3, each of the light-emitting elements 22 of thisembodiment is configured into a geometric shape with at least threecorners. In this embodiment, the geometric share is a quadrilateralshape provided with four corners, and the through holes 23 correspond inposition to the corners of the light-emitting elements 22 or midpointson sides of the light-emitting elements 22 (not shown). Specifically,the stretchable supporting film 21 of this embodiment has a plurality offirst imaginary lines (L1) each located equidistantly between twoadjacent rows of the light-emitting elements 22, i.e., passing throughthe midpoints of the second spacings (S2), and a plurality of secondimaginary lines (L2) each located equidistantly between two adjacentcolumns of the light-emitting elements 22, i.e., passing through themidpoints of the first spacings (S1). The through holes 23 of thisembodiment are periodically formed on the first and second imaginarylines (L1), (L2) and correspond in position to the light-emittingelements 22. More specifically, each of the through holes 23 maycorrespond in position to at least two light-emitting elements 22. Forexample, like in this embodiment, the through holes 23 can be formed atintersections 24 of the first and second imaginary lines (L1), (L2). Inother words, each of the through holes 23 may correspond in position tofour adjacent light-emitting elements 22 in this embodiment. In otherembodiments, the through holes 23 may be periodically formed atpositions on the first and second imaginary lines (L1), (L2) thatcorrespond to the midpoints of the sides of the light-emitting elements22, where the through holes 23 correspond in position to two adjacentlight-emitting elements 22.

The formation of the through holes 23 facilitates uniform stressdistribution throughout the stretchable supporting film 21 while thesame is being stretched, so as to further ensure uniform spacing of thelight-emitting elements 22 along the corresponding direction(s). Assuch, the light-emitting elements 22 can be transferred onto the packagesubstrate 3 in a more precise manner as shown in FIG. 2 after Step (b).It should be noted that a too much higher number of the through holes 23or a too much bigger aperture of the through holes 23 may result inadverse effect on physical properties, such as mechanical strength, ofthe stretchable supporting film 21. Therefore, in preferred embodiments,the through holes 23 are periodically formed at positions whichcorrespond in position to at least two adjacent light-emitting elements22.

While the disclosure has been described in connection with what isconsidered the exemplary embodiment, it is understood that thisdisclosure is not limited to the disclosed embodiment but is intended tocover various arrangements included within the spirit and scope of thebroadest interpretation so as to encompass all such modifications andequivalent arrangements.

What is claimed is:
 1. A method for expanding spacings in alight-emitting element array, comprising: providing a light-emittingelement array unit including a stretchable supporting film, and aplurality of light-emitting elements disposed on the stretchablesupporting film and arranged into a two-dimensional array; andstretching the stretchable supporting film along a first direction and asecond direction so as to expand spacings between the light-emittingelements, wherein the first direction and the second directionrespectively correspond to a row direction and a column direction of thetwo-dimensional array.
 2. The method of claim 1, wherein the step ofstretching the stretchable supporting film is conducted by stretchingthe stretchable supporting film along the first direction followed bystretching the stretchable supporting film along the second direction.3. The method of claim 1, wherein the step of stretching the stretchablesupporting film is conducted by simultaneously stretching thestretchable supporting film along the first and second directions. 4.The method of claim 1, wherein the stretchable supporting film is formedwith a plurality of through holes corresponding in position to thelight-emitting elements.
 5. The method of claim 4, wherein each of thelight-emitting elements is configured into a geometric shape and has atleast three corners, the through holes corresponding in position to thecorners of the light-emitting elements.
 6. The method of claim 4,wherein each of the light-emitting elements is configured into ageometric shape and has at least three sides each having a midpoint, thethrough holes corresponding in position to the midpoints of the sides ofthe light-emitting elements.
 7. The method of claim 4, wherein thestretchable supporting film has a plurality of first imaginary lineseach located equidistantly between two adjacent rows of thelight-emitting elements, and a plurality of second imaginary lines eachlocated equidistantly between two adjacent columns of the light-emittingelements, the through holes being formed on the first and secondimaginary lines of the stretchable supporting film.
 8. The method ofclaim 7, wherein the through holes of the stretchable supporting filmare formed at intersections of the first and the second imaginary lines.9. The method of claim 1, further comprising: attaching a surface ofeach of the light-emitting elements onto a package substrate, followedby removing the stretchable supporting film therefrom, wherein thesurface of each of the light-emitting elements is away from thestretchable supporting film.
 10. The method of claim 9, wherein theremoval of the stretchable supporting film from the light-emittingelements is conducted by irradiating the stretchable supporting filmwith a light having a predetermined wavelength, so as to reduce adhesionstrength between the stretchable supporting film and the light-emittingelements.
 11. The method of claim 9, wherein the removal of thestretchable supporting film from the light-emitting elements isconducted by heating the stretchable supporting film so as to reduceadhesion strength between the stretchable supporting film and thelight-emitting elements.
 12. The method of claim 9, wherein the packagesubstrate is one of a printed circuit board, a TFT substrate, and a CMOSsubstrate.
 13. A light-emitting element array unit comprising: astretchable supporting film; and a plurality of light-emitting elementsthat are disposed on said stretchable supporting film and that arearranged into a two-dimensional array; wherein said stretchablesupporting film is formed with a plurality of through holes thatcorrespond in position to said light-emitting elements.
 14. Thelight-emitting element array unit according to claim 13, wherein each ofsaid light-emitting elements is configured into a geometric shape andhas at least three corners, said through holes corresponding in positionto said corners of said light-emitting elements.
 15. The light-emittingelement array unit according to claim 13, wherein each of saidlight-emitting elements is configured into a geometric shape and has atleast three sides each having a midpoint, said through holescorresponding in position to said midpoints of said sides of saidlight-emitting elements.
 16. The light-emitting element array unitaccording to claim 13, wherein said stretchable supporting film has aplurality of first imaginary lines each located equidistantly betweentwo adjacent rows of said light-emitting elements, and a plurality ofsecond imaginary lines each located equidistantly between two adjacentcolumns of said light-emitting elements, said through holes being formedon said first and second imaginary lines of said stretchable supportingfilm.
 17. The light-emitting element array unit according to claim 16,wherein said through holes of said stretchable supporting film areformed at intersections of said first and second imaginary lines.